Three-axis orientation system



United States Patent [72] inventors Edward E. Shaw; 3,028,807 /1962Burton et al. 244/3.l3 Glen R. Strevey, Boulder, Colo. 3,164,338 1/1965Cooper et al. 244/3.21X [2;] No. 33523931967 3,221,238 11/1965 Unger etal. 235/150.2X E gf 1970 Primary Examiner-Milton Buchler AssistantExaminer-Jeffrey L. Forman [73] Asslgnee ififizg z i CorporationAttorney-Campbell, Harris and ORourke a corporation of Colorado [54]THREBAXIS ORIENTATION SYSTEM ABS'ltRAQT: A system that is automaticallyoperableto orient Chins, 15 Drawing as. a vehicle in three axes. Thesystem first starts desplnnm g of n the vehicle in the roll axis withrespect to a predetermined [52] 244/77; reference source. At apredetermined time after commencen 235/5015: 244/15 244/32 ment ofdespinning, acquisition in the pitch and yaw axes is [51] G05! 1/ 12commenced again with respect to a reference source. After 0f a qui itionin the three axes control is transferred {0 a 810, 810.5, 810.6; 244/77,79, 1s.s., 3.13, 3. tracking mode with line of sight to a preselectedtarget being 235/1501, 150-25 from the aft end of the vehicle. Each axisof the systm com- [56] References Cited prises a core unit captable oflizoth cloarse and filne senrsing with UNITED STATES PATENTS processingcrrcultry or eac mc udrn g a vo tage rmlter, athree-levei contactor,monostabie multlvibrators, and denved 2,737,356 3/1956 Varian et al.244/3,21X rate feedback.

26 1 2.9 7 22 ROLL AXIS COARSE ;I- COARSE SIGNAL 7 7 7 I SENSOR SHAPE 2ROLL AXIS ROLL AXIS ROLL AXIS I VQLVE 27) surname SIGNAL DRIVERS Tunus'rROLL ms RATE 0 AMPLIFIER Pnocssson VAL|VES RATE sue NAL l ssnson SHAPERL l 20 l i statesman J E i ,6 6 7 PITCH -YAW F DETSILCES I 7 43 AXES 23m I 7 arms LING 1 Lg ggxg COARSE cmcunnv i l SENSOR 72 s'fik 4 7 i 7 7 i7 I I I J J oms ews :2 "issue' I 7 l T AMPLIFIER PROCESSOR DR'VERSVALVES l L PITEPNQXIS FINE 52 ssus on I| s ia w e'i i DERIVED) i I 71/cm rr 70 7 i I sc N I seouzucms BYPASS avPAss i I CIRCPITRY I cmcun'nvmuvsn VALVE I 54 L I is was: 29:2 .15 36? I 1 season i SHAPER I 7 7 7 F'J/ I YAW AXIS YAW AXIS -9 VALVE YAW AXIS g 1 ri'fiiii messes mes;

YAVI AXIS FINE 2:. 65 I s ii sim gi ii fi DERIVED I I 5 3' JPATENTEDnEmsmn 35473 1 sum OBUF 1o PITCH AND YAW THRUSTERS EXPERIMENTAPERATURE THRUSTERS LlNE-OF-SIGHT INVENTORS EDWARD E. SHAW BY GLEN R.STREVEY A T TOR/VE Y5 PATENTED DEC] 5 I970 SHEET 08 [1F ATTORNEYS SHEET08 0F mum PATENTED UEC] 5 I978 VQN INVENTORS EDWARD E. SHAW GLEN R.STREVEY BY M/ W J 7ml moos- PATENTED DEC] 5 I976 SHEET 09 0F INVENTOR5EDWARD E. SHAW By GLEN R. STREVEY Mu, A4449; 07w

ATTORNEYS PATENTED DEB] 519m SHEET 10 OF ATTORNEYS THREE-AXISoarsn'ranon SYSTEM BACKGROUND OF THE INVENTION 1. Field of the InventionThis invention relates to control systems for vehicles and relates moreparticularly to three-axis orientation systems for space vehicles.

2. Discussion of the Prior Art Over the last several years muchattention has been given to automatic control of vehicles, includingautomatic control of aircraft and, more recently, automatic control ofspace vehicles. While there was no necessity for stabilizing some earlyvehicles carrying instruments for experimentation, such as instrumentscarried on sounding rockets, for example, it became necessary, ,as theinstruments became more sophisticated, to orient and stabilize thevehicle in order to properly conduct these experiments. Thus, as theinstruments carried in the vehicle became sophisticated, the vehicleitself became more sophisticated by the provision of increasing complexorientation systems progressing from single-axis orientation toorientation in two axes, and finally orientation in all three axesroll,pitch, and yaw.

While three-axis orientation systems have been proposed and/or utilizedheretofore, none of these systems have proved to be completelysuccessful due, at least in part, to the complicated circuitry involved,inability to meet expanded 7 requirements for use, and/or failure independability under all encountered conditions.

In addition, prior orientation systems of this type have generallyrequired the nose cone to be ejected prior to conducting of experiments,since the target to be sensed by a track, or fine, sensor has commonlybeen located in the nose 'cone section.

SUMMARY This invention provides an improved three-axis orientationsystem for a vehicle which includes an improved core unit for each axiswhereby dependable orientation in each axis is quickly achieved withrespect to predetermined references.

It is therefore an object of this invention to provide an improvedsystem for three-axis orientation of a vehicle with respect topredetermined references.

It is another object of this invention to provide an improved three-axisorientation system automatically operable to capture and thereaftertrack a predetermined target.

It is still another object of this invention to provide an improvedthree-axis orientation system having automatic control circuitry forstarting despinning of a vehicle in the roll axis and at a predeterminedlater time, commencing acquisition in the pitch and yaw axes followed bytracking in all three axes of a predetermined target.

It is another object of this invention to provide a three-axisorientation system having an improved core unit for each axis.

It is still another object of this invention to provide an improved coreunit for a three-axis orientation system wherein the core unit includesa voltage limiter, a three-level contactor, monostable multivibrators,and derived rate feedback.

It is another object of this invention to provide an improved three-axisorientation system mounted in a space vehicle in a manner such thatorienting drive is from the nose cone section and sensing of an externaltarget is along a line of sight from the aft section of the vehicle.

With these and other objects in view, which will become apparent to oneskilled in the art as the description proceeds, this invention residesin the novel construction, combination and arrangement of partssubstantially as hereinafter described, and more particularly defined bythe appended claims it being understood that such changes in theembodiments of the herein disclom invention are meant to be included ascome within the scope of the claims.

the invention according to the best mode so far devised for thepractical application of the principles thereof, and in which:

FIG. 1 is a simplified block diagram of the three-axis orien- I tationsystem of the invention;

FIG. 2 is a block diagram in more detail of one axis of the Iorientation system as shown in FIGJ;

FIG. 3 is a perspective view of a space vehicle having the three-axisorientation system of this invention mounted therein;

FIG. 4 is a typical plot illustrating operation of the voltage limitershown in FIG. 2;

FIG. 5 is a representative block diagram utilized for explanation ofderived rate feedback;

FIG. 6 is a phase-plane plot showing a typical acquisition trajectory ofa control system signal;

FIG. 7 is a series of graphs showing the time history of the controlsystem signal of the typical acquisition trajectory as shown in FIG. 6;

FIG. 8 is a phase-plane plot typical of the control system signal duringtarget tracking;

FIG. 9 is a series of graphs showing the time history of the controlsystem signal shown in the phase-plane plot of FIG. 8;

FIGS. 10, 11, and 12, are partial block and schematic diagrams showingin detail the three-axis orientation system illustrated in FIG. 1;

FIG. 13 shows the arrangement of FIGS. 10, 11, and 12, to form acomposite block diagram of the three-axis orientation system of thisinvention;

FIG. 14 is a block diagram showing the pneumatics of the three-axisorientation system; and

FIG. 15 is a block diagram of a single axis of the orientation system ofFIG. 2 to illustrate a modification thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to thedrawings, the numeral 20 indicates generally the three-axis orientationsystem of this invention, which comprises core control units 22, 23, and24, for the roll, pitch, and yaw axes, respectively.

As shown in FIG. 1, roll axis core unit 22 includes a coarse sensor 26and a rate sensor 27. Coarse sensor 26 may be conventional and may be,for example, a gyro package, or attitude reference unit, havingreference sensing over 360. Attitude reference units of this type areoffered on the commercial market and one such unit is offered, forexample, by ACCO, a division of American Chain and Cable CompanyIncorporated. Magnetometers could also be used in place of the gyropackage, if so desired.

The rate sensor is likewise conventional and could be, for example, arate gyro or an output from the gyro reference package. It is alsopossible to utilize a fine sensor in some applications for tracking toachieve better accuracy. Thisunit could also be conventional, and couldbe, for example, an ad-v coarse signal shaper 29 to summing amplifier30. In like manner, the output from rate sensor 27 is coupled throughrate signal shaper 31 and a switch 32 to summing amplifier 30. Switch 32is closed during despinning and acquisition and normally openthereafter. If a fine sensor (not shown) is utilized in the roll axiscore unit, an additional switch (not shown) is utilized to switch eitherthe coarse or fine sensor into the circuit.

The output from summing amplifier 30 is coupled through signal processor33 to valve drivers .34, which control the operation of the roll axisthrust valves 35. The thrust valves will, of course, change the attitudeof the vehicle (indicated by the numeral 36 for the block entitled"Vehicle Dynamical),

and thus change the orientation of the sensors for eachaxisas alsoindicated in FIG. 1. An activating signal (which-resin dicated in FIG. 1can be a signal conventionally produced at the time of vehicleseparation) is coupled to the valve drivers on lead 38 to enable theroll axis error signal coupled to the vehicle drive (thrust valves 35).

In like manner, pitch axis core unit 23 includes a pitch axis coarsesensor 40. which like the roll axis coarse sensor can be a part of theattitude reference gyro unit. The coarse sensor could also be amagnetometer or a solar sensor, for example, both of which are alsoconventional. Pitch axis fine sensor 41 is likewise provided and can bea star tracker, a solar tracker, or a magnetometer, for example, whichunits are again conventional. The output from pitch axis coarse sensor40 is coupled through coarse signal shaper 43 to one contact of switch44. The other contact of switch 44 is connected through fine signalshaper 45 to pitch axis fine sensor 41.

The movable contactor of switch 44 is connected to pitch axis summingamplifier 47, the output of which is coupled through signal processor 48to valve drivers 49. Valve drivers 49 control pitch axis thrust valves50, which like thrust valves 35 cause vehicle deviation, which obviouslycauses a shift in the orientation of the sensors. The outputs from valvedrivers 49 are also coupled through derived rate circuit 52 and fed backto summing amplifier 47, as discussed more fully hereinafter.

Yaw axis core unit 24 likewise includes a coarse sensor 54 and a finesensor 55 which are connected through coarse signal shaper 56 and finesignal shaper 57, respectively, to opposite contacts of switch 58. Themovable contactor of switch 58 is connected through yaw axis summingamplifier 60 and signal processor 61 to valve drivers 62, the outputfrom which controls yaw axis thrust valves 63 to cause deviation of thevehicle to cause a shift in orientation of the sensors. The outputs fromvalve drivers 62 are coupled to derived rate circuit 65, the output ofwhich is fed back through the yaw axis summing amplifier 60 in the samemanner as the derived rate feedback is coupled back to summing amplifier47.

As shown in FIG. 1, an output from coarse signal shaper 29 is alsocoupled to pitch-yaw axes enabling circuitry 67 as is the input signalon lead 38. The output from enabling circuitry 67 is coupled to valvedrivers 49 and 62 in the pitch and yaw core units 23 and 24,respectively, and to sequencing circuitry 69. Two other inputs are alsocoupled to sequencing circuitry 69, one being from coarse signal shaper43 in the pitch axis coarse unit and the other being from coarse signalshaper 56 in the yaw axis core unit.

One output from sequencing circuitry 69 is coupled back to pitch axisfine sensor 41 and yaw axis fine sensor 55 to enable the same, while asecond output is coupled to bypass driver 70, which is utilized to drivebypass valve 71 to bypass the regulator in the pneumatic system. Inaddition, sequencing circuitry 69 is used to control the position ofswitch 32 in the roll axis core unit and is used to control switches 72and 73. Switch 72 connects a signal indicating scan input to the coarsesignal shaper 43 in the pitch axis core unit, while switch 73 connectsthe signal indicating scan input to coarse signal shaper 56 in the yawaxis core unit. Switches 72 and 73 are closed when the fine sensors failto sense the presence of a target to cause scan to coarse targetsearching. The switches and accompanying scan circuitry 74 could also beutilized if a plurality of targets are to be sequentially acquired andtracked.

As also indicated in FIG. 1, outputs from pitch axis fine sensor 41 areused to control switches 44 and 58 in the pitch axis and yaw axis coreunits, respectively, to switch the orientation system between theacquisition (coarse sensing) mode and the tracking (fine sensing) mode.

Referring now to FIG. 2, a block diagram of pitch axis core unit 23 isshown in more detail, this axis being also illustrative of the yaw axisand basically to the roll axis (without feedback), as can be appreciatedfrom FIG. 1. As can be seen by comparison of the pitch axis core unit asshown in FIG. 2 with the simplified block diagram of the pitch axis coreunit as illustrated in FIG. I, coarse signal shaper 43 includesamplifier and demodulator 75, voltage limiter 76, and lead-lag network77,

while fine signal shaper 45 includes an amplifier 79 and a noise filter80, all of which may be conventional.

Amplifier and demodulator 75 conditions input signals from the coarsesensor for system compatibility while amplifier 79 conditions inputsignals from the fine sensor for system compatibility. Such a signalcould be, for example, a produced output signal having sufficientmagnitude to drive the next state. A demodulator is not necessary in allapplications, but would be used, for example, with an attitude referenceunit or a magnetometer.

Voltage limiter 76 is used conventionally to limit voltage to apredetermined range, which as illusuated in FIG. 4, is genericallyexpressed as a range of between +E, and E, from +0 to Lead-lag network77 serves to ensure system stability and this network follows thegeneral ratio:

aT S+1 T S+1 (I) wherein a is a constant lead, T is a time constant forthe acquisition mode, and S is the LaPlace transform.

Noise filter 80 is not necessary under all conditions but, if utilizedfollows the general ratio:

wherein T 6 is the time constant for the filter, and S is the LaPlacetransform.

As also shown from comparison of FIGS. 1 and 2, pitch axis signalprocessor 48 includes contactor 82, monostable multivibrators 83, and ORgates 84.

Contactor 82 is a three-level contactor which gives a positive constantvoltage output, a negative constant voltage output, or a zero output,depending upon the magnitude and polarity of the signal input, and couldalso be considered threshold discriminators, as is conventional.

Monostable, or one-shot, multivibrators 83 are conventional and thelength of firing depends upon the time needed for proper operation ofvehicle thrust in junction with valve drivers 49, which may beconventional power transistors. It has been found that a 14 millisecondmonostable multivibrator is satisfactory for use in the system of thisinvention.

As shown in FIG. 2, OR gates 84 receive the output from one-shotmultivibrators 83 as well as a direct output from the contractor, whichsignal bypasses multivibrator 83. This assures that there will be anoutput from the OR gates to the valve drivers should the signal from thecontractor be of longer duration than the output from the multivibrator,and

yet assures a minimum length signal (from the multivibrator) to causethrust in the desired direction.

As also shown in FIG. 2, derived rate feedback circuit 52 includesacquisition derived rate 87 and track derived rate 88, depending uponthe position of switch 86, which is constrained to movement along withswitch 44 as is indicated in FIG. 2. Derived rate feedback is utilizedto provide dampening signals for system stability purposes and tosuppress noise.

Derived rate is a means for generating rate information from signalsgenerated internally of the orientation system and is based on theconsideration that if the torque and inertia about an axis is known, theoutput of the contractor is directly proportional to the accelerationabout that axis. Vehicle rate is directly proportional to the timeintegral of this acceleration signal. In the system of this invention,derived rate is mechanized by coupling the contactor output through alag network the output of which is proportional to the change in vehiclerate if the acceleration thrust time is small relative to the lagnetwork time constant. Referring to FIG. 5, which shows a derived rateblock diagram,

wherein E is the voltage output of the derived rate network, K, is thegain of the derived rate network, a is the contactor output voltage, Iis the acceleration thrust time, 1 is the time constant of the derivedrate lag network, and is the angular change of the system.

As shown from FIG. and the equations with respect thereto, the rateinfonnation that is available from a derived rate feedback network isonly that rate generated by thruster force.

From the foregoing, it can be seen that the derived rate network foracquisition mode follows the ratio:

wherein K is the gain of acquisition feedback, T is the time constantfor the acquisition decimal rate, and S is the LaPlace transform.

In the like manner, the track derived rate follows the ratio:

Kn Tws+ 1 (5 wherein K is the gain of track feedback, T is the timeconstant for track feedback, and S is the LaPlace transform.

An anomaly of derived rate feedback is a decaying rate signal when thethrusters are inactive and vehicle rate is constant. This effect ispresent during performance and can be used to advantage, particularly inthe track mode, to achieve both noise suppression and stability control.

FIG. 6 is a phase-plane plot of a typical acquisition trajectory for thesystem of this invention, while FIG. 7 shows a time history of controlsignals for the typical trajectory shown in FIG. 6. As utilized therein,vehicle acceleration with thruster valves activated is 0.5 radian/secthe derived rate gain is 0.233, the switching point 8 is 0.6 and thelimiter saturation level is 4. These values are typical for the systemof this invention for pitch and yaw axis acquisition. As shown in thephaseplane plot of FIG. 5, the trajectory is not a minimum timetrajectory, but is slightly slower to enable use of a system which ishighly adaptable for different performance requirements and errorsensors.

The phase-plane (shown in FIG. 6) exhibits a form of common velocityledge during the early portion and the reticence stepping action (aboutnull) that is characteristic of highly damped systemsusing a three-levelcontactor with hysteresis. Examination of the time plot (shown in FIG.7) shows the output at the derived rate network increasing during theinitial thrust phase until it is large enough to overcome the limiteroutput voltage and deactivate the thruster valves. At this time, if arate sensor were used, the vehicle velocity would remain constant untilthe vehicle position becomes smaller than the limiter saturation level.However, because of the decaying output voltage of the derived ratenetwork when a thruster is off, the thruster pulses during the time thelimiter is in a saturated condition. When the vehicle position is lessthan the limiter saturation level, the opposing thruster is immediatelyactivated to reduce the vehicle velocity. At the completion of thisthrust phase, both the position error and vehicle velocity are small andthe vehicle follows the reticence trajectory toward null where a limitcycle is established.

FIG. 8 is a phase-plane plot of a typical orientation system signalduring target tracking, while FIG. 9 shows a series of graphsillustrating the time history of this signal during target tracking. Asutilized, the vehicle acceleration is 0.02 radian/sec, the derived rategain is 0.0233, the switch point is set at arc seconds, and the minimumthrust impulse causes a change of rate of 58 are seconds per second.

The phase-plane plot shown in FIG. 8 has what might be termed a limitcycle within a limit cycle caused by a difference in the positive andnegative impulses, as a result of different monostable times ordifferent positive and negative thruster characteristics.

An examination of FIG. 8 shows that the two contributions of derivedrate during limit cycle operation are:

1. During the thrust phase the equivalent hysteresis provided by themonostable-derived rate combination suppresses system and sensor noise(this is evident by examination of the waveforms of FIG. 9 which showthat the E voltage is rapidly changed during the thrust phase); and

2. proper scaling of the decaying derived rate voltage (when thethruster is off) provides the necessary rate signal required for vehicledamping and limits cycle stability. Freedom of choosing both the derivedrate time constant and gain is used at this time to satisfy the noiseand rate requirements. The use of derived rate in the track modeeliminates the need for lead compensation and the inherent noise gainassociated with this type of compensation, thereby relaxing the noiserequirements for the fine sensor. In addition, fuel consumption isminimized utilizing the system of this invention.

Referring now to FIGS. 10, 11 and 12, which together (as shown by FIG.13) form a composite partial block and schematic diagram of thethree-axis control orientation system of this invention as shown inFIG. 1. As shown in FIG. 10, roll axis coarse sensor 26 is indicated asbeing an attitude reference unit, the roll synchro output of which iscoupled to demodulator and amplifier (which together with lead-lagnetwork 91 and voltage limiter 96 form coarse signal shaper 29).

The output from demodulator and amplifier 90 is coupled to lead-lagnetwork 91, which network has a resistor 92 connected in parallel withserially connected resistor 93 and capacitor 94. The output fromlead-lag network 91 is then coupled to voltage limiter 96, which limiterincludes an amplifier 97 having a resistor 98 and back-to-back zenerdiodes 99 and 100 connected thereacross.

The output from voltage limiter 96 is coupled through re sistor 102directly to roll axis summing amplifier 30, which summing amplifier hasa resistor 103 connected thereacross.

Rate sensor 27 is indicated in FIG. 10 as being an attitude referenceunit-the DC Tach output from which is coupled to amplifier 104 (of finesignal shaper 31) through a resistor 105 with the amplifier having aresistor 106 thereacross. The output of amplifier 104 is coupled throughresistor 107 to switch 32 which is connected at the other side tosumming amplifier 30.

As also shown in FIG. 10, the contactor (roll axis signal processor 33)in effect is a positive switching discriminator 110 and a negativeswitching discriminator 111, which are connected to receive the outputfrom summing amplifier 30. The output from the positive switchingdiscriminator is coupled to valve driver 113 and the negative switchingdiscriminator is coupled to valve driver 114, which taken together formthe valve drivers 34 as indicated in FIG. 1.

The output from positive roll axis valve driver 113 is coupled topositive roll axis valve 116, while the output from negative roll axisvalve driver 114 is coupled to the negative roll axis valve 117, which,of course, effect vehicle dynamics as indicated in FIG. 1. Both thepositive and negative roll axis valve drivers 113 and 114 are activatedby a roll axis enable signal on lead 38.

Referring now to FIG. 11, coarse sensor 40 is shown to be an attitudereference unit with the pitch synchro output. being coupled through acontrol transformer to demodulator and amplifier 75. Control transformer120 is utilized for preprogramming the line of sight to the vicinity ofa desired target. Although not shown, the roll is also preprogramrned toassure acquisition of the predetermined target.

The output from the amplifier and demodulator 75 is then coupled tovoltage limiter 76, as shown in FIG. 1 1, includes an amplifier 122having an input resistor 123 and resistor 124 and back-to-back zenerdiodes 125 and 126 connected in parallel therewith. The output fromvoltage limiter 76 is then coupled to lead-lag network 77 which includesa resistor 128 having connected in parallel therewith serially connectedresistor 129 and capacitor 130. The output from the lead-lag network 77is then coupled to switch 44.

As also indicated in FIG. 11, fine sensor 41 may be a star trackerhaving acquisition and track modes as is conventional. The output fromthe star tracker (either mode as shown) is coupled to network 80, whichincludes resistor 132 connected to one contact of switch 133 andresistor 134 having serially connected resistor 135 and capacitor 136 inparallel therewith connected to the other contact. The movable contactorof switch 133 is positioned depending upon the acquisition of the trackmode of the star tracker.

The output from network 80 is taken from the movable contactor of switch133 and coupled to amplifier 79, which has a resistor 138 connectedthereacross and a resistor 139 at the output side through which theamplifier is connected to one contact of switch 44.

The movable contactor of switch 44 is connected to summing amplifier 47which has a resistor 141 connected thereacross. The output from summingamplifier 47 is then coupled to contactor 82 which, as shown in FIG. 11,in effect is a positive switching discriminator 143 and a negativeswitching discriminator 144. The output from positive switchingdiscriminator 143 is then coupled to one-shot multivibrator 146 whilethe output from the negative switching discriminator 144 is coupled toone-shot multivibrator 147 (the one-shot multivibrators 146 and 147taken together being the monostable multivibrators 83 indicated in FIG.2). The output from one-shot multivibrator 146 is one input to OR gate148, while the output from one-shot multivibrator 147 is coupled to oneinput of OR gate (OR gates 148 and 149 being the OR gates 84 indicatedin FIG. 2). The second input to the OR gates is coupled directly theretofrom the positive and negative switching discriminators 143 and 144.

The output from OR gate 148 is coupled to positive pitch axis valvedriver 151, while the output from OR gate 149 is coupled to negativepitch axis valve driver 152 (which drivers together are the drivers 49shown in FIG. 2). The output from pitch axis valve driver 151 is coupledto positive pitch valve 153, while the output from negative pitch axisvalve driver 152 is coupled to negative pitch valve 154 (which areindicated as the vehicle control thrust valves 50 of FIG. 2).

The output from pitch axis valve drivers 151 and 152 are coupled incommon through resistor 156 to amplifier 157 in the derived ratefeedback path. Amplifier 157 has connected, in parallel therewith, aresistor 158, a capacitor 159, and a capacitor 160, with capacitor 160being connected into the circuit through a switch 161. Switch 161 isone-half of switch 86 of FIG. 2 and is closed when the fine sensor isoperable. The output from amplifier 157 is then coupled through resistor163, having connected in parallel therewith a resistor 164 which isconnected into the circuit by a switch 165 (switch 165 being the otherhalf of switch 86 indicated in FIG. 2). The derived rate is then coupledback to the input side of the summing amplifier through switch 166.

Referring now to FIG. 12, which shows the yaw axis core unit 24, coarsesensor 54 is indicated as being an attitude reference unit with the yawsynchro output being coupled to demodulator and amplifier 168(demodulator and amplifier 168 along with voltage limiter 170 andlead-lag network 177 form coarse signal shaper 56). The output fromdemodulator and amplifier 168 is coupled to voltage limiter 170 whichincludes an amplifier 171 having an input resistor 172 and resistor 173and back-to-back zener diodes 174 and 175 connected in paralleltherewith. The output from voltage limiter 170 is then coupled tolead-lag network 177, which includes a resistor 178 having connected inparallel therewith serially connected resistor 179 and capacitor 180.The output from lead-lag network 177 is then coupled to one contact ofswitch 58.

Yaw axis fine sensor 55 may, as indicated in FIG. 12, be a star trackerhaving acquisition and track modes as does the pitch fine sensor. Theoutput from fine sensor 55 is coupled to network 182, which togetherwith amplifier 189 forms fine signal shaper 57. Network 182 includes aresistor 183 connected to one contact of switch 184, while the othercontact of the switch is connected to resistor 185 having connected inparallel therewith serially connected resistor 186 and capacitor 1187.Switch 184 is positioned according to whether the acquisition or trackmode of the star tracker is utilized.

The output from the noise filter 182 is coupled to amplifier 189.Amplifier 189 has a resistor 190 connected thereacross and a resistor191 at the output connecting the amplifier to the other contact ofswitch 58.

The output of switch 58 is connected to yaw axis summing amplifier 60,which has a resistor 192 connected thereacross. The output from summingamplifier 60 is then coupled to the contactor, which, as indicated inFIG. 12, is in effect a positive switching discriminator 194, andnegative switching discriminator 195, the outputs of which, in'turn, areconnected to one-shot multivibrators 196 and 197, respectively. Theoutput from one-shot multivibrator 196 is connected to one input of ORgate 198, while the output from one-shot multivibrator 197 is connectedto one input of OR gate 199. In addition, OR gates 198 and 199 receive adirect input from switching amplifier discriminators 194 and 195,respectively, as brought out hereinabove with respect to the pitch axiscore unit. The contactor, one-shot multivibrators and OR gates togetherform the yaw axis signal processor of FIG. 1.

The output from OR gate 198 is coupled to positive yaw axis valve driver201, while the output from OR gate 199 is coupled to negative yaw axisvalve driver 202 (which valve drivers together are valve drivers 62 ofFIG. 1). The output from positive yaw axis driver 20] is coupled topositive yaw valve 204, while negative yaw axis valve driver 202 iscoupled to negative yaw valve 205 (which valves together are the thrustvalves of FIG. 1).

The outputs from positive yaw axis valve driver 201 and negative yawaxis valve driver 202 are connected in common through resistor 207 toamplifier 208 in the yaw axis derived rate feedback path. Amplifier 208has connected in parallel therewith a resistor 210, a capacitor 211, anda capacitor 212, with capacitor 212 being connected into the circuit bymeans of switch 213. Switch 213 is closed when the star tracker is inthe track mode.

The output from amplifier 208 is then coupled to resistor 215, havingconnected in parallel therewith a resistor 216 which is connected intothe circuit by means of switch 217 (which is operated in conjunctionwith switch 213 for track and to be closed when derived rate is in thetrack mode). The output from resistor 215 is then coupled to the inputside of summing amplifier 60 through switch 218. Switches 166 and 218are connected operatively with switches 133 and 184, respectively.

The separation signal input on lead 38, as shown in FIG. 10, is coupledto roll axis gated discriminator 220, which discriminator receives asecond input from demodulator and amplifier 90. The output from gateddiscriminator 220 is directly coupled to AND gate 222, the second inputof which is coupled from the gated discriminator through delay circuit223. The output from AND gate 222 is then coupled through lead 224 topitch axis valve drivers 151 and 152 and yaw axis valve drivers 201 and202.

The output from AND gate 222 is also coupled through lead 225 to pitchgated discriminator 227, which discriminator receives a second inputfrom demodulator and amplifier 75, as shown in FIG. 11. The output frompitch gated discriminator 227 is coupled to AND gate 228, which receivesa second input from yaw gated discriminator 230. Yaw gated discriminator230 receives in input from AND gate 222 through lead 225 and receives asecond input from demodulator and amplifier 168. The output from ANDgate 228 is directly coupled to AND gate 232, the second input of ANDgate 232 being provided from AND gate 228 through delay circuit 233.

The output from AND gate 232 is coupled to the pitch axis fine sensorand yaw axis fine sensor as an enabling signal through lead 234. Anotheroutput from gate 232 is coupled to pneumatic bypass valve driver 70,which is connected to pneumatic bypass valve 71, as shown in FIG. 11.Still another output from AND gate 232 is coupled to roll axis tachswitch driver 239, the output of which is coupled through lead 240 tocontrol the positioning of switch 32, as indicated in FIG. 10. A finaloutput from AND gate 232 is coupled to gated scan discriminator 242, theoutput of which is coupled to AND gate 243 which receives a second inputfrom gated scan discriminator 242 through delay circuit 244. The outputfrom AND gate 243' is coupled through-lead 246 to control thepositioning of switches 72 and 73. Switch 72 connects the scan inputfrom scan circuitry 74 through resistor 251 to voltage limiter 76, whileswitch 73 connects the scan input through resistor 252 to voltagelimiter 170.

An output from star tracker 41 indicating star presence is also coupledto switches 44, 58, 133, 166, 184, and 218, to control the positioningof the same, while an output indicating mode sequence is coupled to thesame switches to reset the same as well as to switches 161, 165, 213,and 127, to control the positioning of these switches.

Although not shown, an input signal could also be coupled to thesummingamplifier to provide automatic scan or simple offsetduring targettracking.

Referring now to FIG. 14, which shows the pneumatics of the system, asource of drive, or thrust, 260, such as nitrogen, for example, iscoupled through a regulator 261 to the various valves indicated in FIGS;10, 11 and 12. Regulator 261 allows a predetermined flow yieldably lowthrust during track, for ex ample, of 0.2 lbs. During acquisition, theregulator is bypassed by bypass valve 71 to enable a relatively largethnist during this period, for example, of 4 lbs. A fill valve 263 isalso preferably provided, as shown in FIG. 14.

In operation, the roll enabling signal occuring at separation causescommencement of despinning of the vehicle about the roll axis. Atimewise later output from the pitch-yaw enabling circuitry then causescommencement of acquisition in the pitch and yaw axes. Fine sensing iscommenced by the sequencing circuitry after the target is acquired andtracking of the acquired target is thereafter maintained. The errorsignals produced by such core unit cause the thrust valves to open todeviate the vehicle in the direction required to reduce and eliminatethe error signal along the particular axis.

Referring now to FIG. 15 which shows a modified embodiment of the pitchaxis core unit of FIGS. 2 and 11, the modifications include fine sensor41 being coupled to AGC amplifier 267, which receives a control inputfrom amplifier 269 and provides an output to amplifier 79. In addition,a target sensor 271 is provided, the output of which is coupled throughamplifier 269 to gated discriminator 273, the second input to discriminator 273 being supplied by the separation input signal.

The output from gating discriminator 273 is coupled to AND gate 275,which gate receives a second input from discriminator 277 which isconnected to receive the output signal from amplifier and demodulator75. The output from the AND gate 275 is coupled to the base offield-effect transistor 279, which is connected to a 8+ voltage sourceat one side through resistor 281 and connected at the other side to theinput of voltage limiter 76. The output from gated discriminator 273 isalso coupled to bypass valve driver 70 and to switch driver 283 leadingto bypass valve 71 and roll axis switch 32, respectively.

Target sensor 271 is thus utilized for automatic gain control for thefine sensor and the field effect transistor 279 provides an etfectiveerror signal output to continue movement of the vehicle until such timeas the coarse sensors pick up a signal.

From the foregoing, it can be seen that this invention provides animproved orientation system and more particularly an improved three-axisorientation system.

We claim:

1. A three-axis orientation system for a vehicle, said systemcomprising: first axis sensing and processing circuitry for developingan error signal indicative of deviation from a predetermined referencewith respect to said first axis; second axis sensing and processingcircuitry for developing an error signal indicative of deviation from apredetermined reference with respect to said second axis, said secondaxis sensing and processing circuitry including derived rate feedbackmeans; third axis sensing and processing circuitry for developing anerror signal indicative of deviation from a predetermined reference withrespect to said third axis, said third axis sensing and processingcircuitry including derived rate feedback means; drive means; andcontrol. means for automatically sequencing said sensing and processingcircuitry to quickly and efficiently stabilize said vehicle inconjunction with said derived rate feedback means.

2. The system of claim I wherein said vehicle is a space vehicle andwherein said stabilized axes are roll, pitch and yaw axes with saidderived rate feedback means being connected in said pitch and yaw axes.

3. The system of claim 1 wherein each said sensing and processingcircuitry includes a voltage limiter and a contactor.

4. The system of claim 2 wherein said pitch and yaw axes sensing andprocessing means includes a voltage limiter, a contactor, and a pair ofmonostable multivibrators.

5. A core unit for an attitude orientation system, said core unitcomprising: sensing means for producing an error signal when said sensordeviates from a predetermined reference; contactor means for producing apositive output signal when an error signal greater than a preselectedmagnitude is received of one predetermined polarity, for producing anegative output signal when an error signal greater than a preselectedmagnitude is received of the opposite polarity from said onepredetermined polarity, and for producing no output signal when no errorsignal is received that has a magnitude greater than said preselectedmagnitude; monostable multivibrator means for receiving the output fromsaid contactor and producing an output signalin response to receipt ofan error signal therefrom; and drive means for receiving the output fromsaid multivibrator means and causing movement in response thereto in adirection to reduce and eliminate said error signal.

6. The core unit of claim 5 wherein said multivibrator means includes apair of one-shot multivibrators one of which is triggered by a positiveerror signal from said contactor and the other of which is triggered bya negative error signal from said contactor. v

7. The core unit of claim 5 wherein saidsensing means includes a voltagelimiter the output of which is connected with said contactor means.

8. The core unit of claim 5 further characterizedby'target sensing meansand target signal processing means connected with said target sensingmeans to' produce anerrorsignal in the absence of a received signal bysensing means to cause deviation of said vehicle to facilitate targetacquisition.

9. The core unit of claim 8 wherein said target signal processing meansincludes a discriminator connected with said sensing means and a fieldeffect transistor, said transistor being triggered by said discriminatorwhen no target is sensed by said sensing means.

10. The core unit of claim 8 further characterized by an AGC amplifierconnected with said sensing means and said target signal processingmeans for automatic gain control of said core unit.

11. A core unit for an attitude orientation system, said core unitcomprising: sensing means for producing an error signal when said sensordeviates from a predetermined reference; summing means; contactor meansfor producing a positive output signal when an error signal greater thana preselected magnitude is received of one predetermined polarity, for

producing a negative output signal when an error signal. greater than apreselected magnitude is received of the opposite polarity to said onepredetermined polarity, and for in response thereto in a direction toreduce said error signal; and derived rate feedback means connectedbetween said multivibrator means and said summing means to providedamping feedback signals to enhance system stability and reduce noise.

12. A core unit for an attitude orientation system, said core unitcomprising: coarse sensing means for producing an output signal whensaid sensor deviates from a predetermined coarse reference; fine sensingmeans for producing an output signal when said sensor deviates from apredetermined fine reference; switch means for switching between saidsensing means; contactor means connected with said switching means forproducing a positive output signal when an error signal is received ofone predetermined polarity and greater than a preselected magnitude, forproducing a negative output signal when an error signal is received ofthe opposite polarity of said one predetermined polarity and greaterthan a preselected magnitude, and for producing no output signal when noerror signal is received that has a magnitude greater than saidpreselected magnitude; monostable multivibrator means for receiving theoutput from said contactor and producing an output signal in response toreceipt of an error signal therefrom; and control means connected withsaid switching means for connecting said fine sensing means into saidcore unit after an output from said coarse sensing means has produced anoutput signal.

13. The core unit of claim 12 wherein said coarse sensing means includesa voltage limiter the output of which is connected with said switchingmeans, and further characterized by summing means connected between saidswitching means and said contactor and derived rate feedback meansconnected between said multivibrator means output and said summingmeans.

14. A three-axis orientation system for a space vehicle, said systemcomprising: first sensor means for producing an output signal when adeviation occurs with respect to a predetermined acquisition referencein the roll axis of said space vehicle; second sensor means forproducing an output signal when a deviation occurs with respect to apredetermined rate reference in the roll axis of said space vehicle;first switching means; first signal processing means connected with saidfirst switching means to receive the output signal from one of saidfirst and second sensing means and producing a positive error signal ifdeviation occurs in one direction and a negative error signal ifdeviation occurs in the opposite direction; a first pair of valvedrivers connected with said first signal processing means, one of saiddrivers receiving said positive error signal and the other of saiddrivers receiving said negative error signal; a first pair of thrustvalves connected with said first pair of valve drivers to cause vehicledeviation along said roll axis in a manner opposing said deviationcausing said error signal to be produced, third sensing means forproducing an output signal when a deviation occurs with respect to apredetermined acquisition reference in the pitch axis of said spacevehicle; fourth sensing means for producing an output signal when adeviation occurs with respect to a predetermined track reference in thepitch axis of said space vehicle; second switching means; second signalproducing means connected with said second switching means to receivethe output signal from one of said third and fourth sensing means andproducing a positive error signal if deviation occurs in one directionand a negative error signal if deviation occurs in the oppositedirection; a second pair of valve drivers connected with said secondsignal processing means, one of said valve drivers receiving saidpositive error signal and the other of said valve drivers receiving saidnegative error signal; a second pair of thrust valves connected withsaid second pair of valve drivers to cause vehicle deviation along saidpitch axis in a manner opposing said deviation causing said error signalto be produced; fifth sensing means for producing an output signal whena deviation occurs with respect to a predetermined acquisition referencein the yaw axis of said space vehicle;

sixth sensing means for producing an output signal when a deviationoccurs with respect to a predetermined track reference in the yaw axisof said space vehicle; third switching means; third signal processingmeans connected with said third switching means to receive the outputsignal from one of said fifth and sixth sensing means and producing apositive error signal if deviation occurs in one direction and anegative error signal if deviation occurs in the opposite direction; athird pair of valve drivers connected with said third signal processingmeans, one of said drivers receiving said positive error signal and theother of said drivers receiving said negative error signal; a third pairof thrust valves connected with said third pair of valve drivers tocause vehicle deviation along said yaw axis in a manner opposing saiddeviation causing said error signal to be produced; and control meansconnected with said switching means for causing automatic and sequentialacquisition and tracking with respectto all three axes of said spacevehicle.

15. The orientation system of claim 14 wherein said first, third andfifth sensing means includes a voltage limiter and a lead-lag network.

16. The orientation system of claim 14 wherein said signal processingmeans includes a summing amplifier, a contactor, a pair of monostablemultivibrators and a derived rate feedback connected between the outputof said monostable multivibrators and said summing amplifier.

17. The orientation system of claim 16 wherein said signal processingmeans includes a pair of OR gates each of which receives the output fromone of said monostable multivibrators and a direct output from saidcontactor.

